The only son, albeit illegitimate, of Magnus II, Haakon III Magnusson succeeded in Hordaland more by being in the right place at the right time than right of succession (which was woolly enough at the time).

On the death of Olaf II Kyrre in 1093 Hordaland appeared split in its loyalties. Parts supported Olaf's illegitimate son Magnus III whilst others backed Haakon. Magnus was abroad campaigning in Scotland however and this allowed Haakon to claim the crown. Magnus duly returned to Hordaland though a civil war was averted and it looks as if the cousins agreed to act as co-kings, much as their fathers had done.

The agreement had little chance to see if it would hold. Haakon died in March 1094 leaving Magnus in sole control over the country. Some historians have judged this a very handy and timely death but there is no hint of foul play in the historical record.

His own life is little commented on by the chroniclers who only mention him when discussing Magnus III's early reign. It is unknown if he had a wife or any children and neither do any portraits remain.